CHAPTER III.

STRUGGLE FOR EXISTENCE.

Its bearing on natural selection-The term used in a wide sense
Geometrical ratio of increase-Rapid increase of naturalised
animals and plants-Nature of the checks to increase-Compe-
tition universal-Effects of Climate Protection from the
number of individuals — Complex relations of all animals and
plants throughout nature- Struggle for life most severe between
individuals and varieties of the same species; often severe be-
tween species of the same genus -
The relation of organism to
organism the most important of all relations

CHAPTER IV.

NATURAL SELECTION.

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.. Page 63-82

Natural Selection-its power compared with man's selection - its
power on characters of trifling importance — its power at all ages
and on both sexes Sexual Selection - On the generality of inter-
crosses between individuals of the same species — Circumstances
favourable and unfavourable to Natural Selection, namely,
intercrossing, isolation, number of individuals - Slow action-
Extinction caused by Natural Selection-Divergence of Cha-
racter, related to the diversity of inhabitants of any small area,
and to naturalisation - Action of Natural Selection, through
Divergence of Character and Extinction, on the descendants
from a common parent→ Explains the Grouping of all organic
beings - Advance in organisation-Low forms preserved -
Objections considered-Indefinite multiplication of species-
Summary
83-147

CHAPTER V.

LAWS OF VARIATION.

Effects of external conditions-Use and disuse, combined with
natural selection; organs of flight and of vision - Acclimatisa-
tion-Correlation of growth-Compensation and economy of
growth-False correlations - Multiple, rudimentary, and lowly
organised structures variable-Parts developed in an unusual
manner are highly variable: specific characters more variable
than generic: secondary sexual characters variable-Species of
the same genus vary in an analogous manner - -Reversions to
long-lost characters — Summary
148-188

-

CHAPTER VI.

DIFFICULTIES ON THEORY,

-

Difficulties on the theory of descent with modification-Transitions-
Absence or rarity of transitional varieties-Transitions in habits
of life -Diversified habits in the same species-Species with
habits widely different from those of their allies-Organs of
extreme perfection - Means of transition-Cases of difficulty -
Natura non facit saltum-Organs of small importance - Organs
not in all cases absolutely perfect — The law of Unity of Type
and of the Conditions of Existence embraced by the theory of
Natural Selection..
Page 189-226

CHAPTER VII.

INSTINCT.

Instincts comparable with habits, but different in their origin.
Instincts graduated — Aphides and ants- Instincts variable-

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-

Domestic instincts, their origin-Natural instincts of the cuckoo,
ostrich, and parasitic bees-Slave-making ants - Hive-bee, its
cell-making instinct - Changes of instinct and structure not
necessarily simultaneous - Difficulties on the theory of the
Natural Selection of instincts -Neuter or sterile insects -
Summary

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227-266

CHAPTER VIII.

HYBRIDISM.

-

Distinction between the sterility of first crosses and of hybrids —
Sterility various in degree, not universal, affected by close inter-
breeding, removed by domestication-Laws governing the sterility
of hybrids-Sterility not a special endowment, but incidental
on other differences-Causes of the sterility of first crosses and of
hybrids- Parallelism between the effects of changed conditions
of life and of crossing-Fertility of varieties when crossed
and of their mongrel offspring not universal-Hybrids and
mongrels compared independently of their fertility - Summary

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267-301

CHAPTER IX.

ON THE IMPERFECTION OF THE GEOLOGICAL RECORD.

-

On the absence of intermediate varieties at the present day - On
the nature of extinct intermediate varieties; on their number—
On the vast lapse of time, as inferred from the rate of deposi-
tion and of denudation On the poorness of our paleontological
collections - On the denudation of granitic areas-On the
intermittence of geological formations-On the absence of
intermediate varieties in any one formation - On the sudden
appearance of groups of species —On their sudden appearance in
the lowest known fossiliferous strata..
Page 302-337

CHAPTER X.

ON THE GEOLOGICAL SUCCESSION OF ORGANIC BEINGS.

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On the slow and successive appearance of new species-On their
different rates of change-Species once lost do not reappear-
Groups of species follow the same general rules in their appear-
ance and disappearance as do single species-On Extinction ·
On simultaneous changes in the forms of life throughout the
world-On the affinities of extinct species to each other and to
living species-On the state of development of ancient forms-
On the succession of the same types within the same areas—
Summary of preceding and present chapter,

CHAPTER XI.

GEOGRAPHICAL DISTRIBUTION.

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338-375

Present distribution cannot be accounted for by differences in phy-
sical conditions Importance of barriers-Affinity of the pro-
ductions of the same continent- Centres of creation Means
of dispersal, by changes of climate and of the level of the land,
and by occasional means-Dispersal during the Glacial period
co-extensive with the world
376-413

CHAPTER XII.

GEOGRAPHICAL DISTRIBUTION-continued.

Distribution of fresh-water productions - On the inhabitants of
oceanic islands - Absence of Batrachians and of terrestrial Mam-
mals-On the relation of the inhabitants of islands to those of
the nearest mainland-On colonisation from the nearest source
with subsequent modification-Summary of the last and pre-
sent chapter
Page 414-442

CHAPTER XIII.

MUTUAL AFFINITIES OF ORGANIC BEINGS: MORPHOLOGY:
EMBRYOLOGY: RUDIMENTARY ORGANS.

CLASSIFICATION, groups subordinate to groups - Natural system-
Rules and difficulties in classification, explained on the theory of
descent with modification - Classification of varieties - Descent
always used in classification - Analogical or adaptive characters

·Affinities, general, complex and radiating-Extinction se-
parates and defines groups-MORPHOLOGY, between members
of the same class, between parts of the same individual —
EMBRYOLOGY, laws of, explained by variations not supervening
at an early age, and being inherited at a corresponding age
– RUDIMENTARY ORGANS; their origin explained — Summary
443-491

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-

favour

CHAPTER XIV.

RECAPITULATION AND CONCLUSION.

Recapitulation of the difficulties on the theory of Natural Selection
Recapitulation of the general and special circumstances in its
Causes of the general belief in the immutability of
species How far the theory of natural selection may be
extended-Effects of its adoption on the study of Natural
history-Concluding remarks..

INDEX

492-525

-527-538

INSTRUCTION TO BINDER.

The Diagram to front page 123, and to face the latter part of the

Volume.